I saw Chad's behaviour in that scene as less "he can't put in a token effort" and more "he's actually a clueless fuck". Seemed pretty obvious he genuinely didn't see a problem with the kiss, and when Sage starts going "you should fuck me", he looks at her disappointed like a parent does a child. He just seems tired of her shit.
Couple that with Chad later finally being happy in the dorms, away from her. Makes total sense he dumps her a week later after its clear she either won't or can't help him.
So on the one hand he's a skilled enough manipulator to hide is affair from her until Week 1 and still smooth things over after she finds the panties, but on the other hand he doesn't notice her all but putting a ribbon on her tits? Color me skeptical.
Also, if he's just tired of her shit, why not say that when he breaks up? He's constantly refusing to meet her gaze as he goes through the whole "It's not you, it's me" routine. If he's a clueless, socially inept fuck who doesn't care about Sage, why the song and dance?
EDIT:
Is this true!? Also I don't remember playing episode 6. I guess I am in for a treat.
No, it's not true. Best guess is Episode 7 releases April 16, +/- 1 week, but nothing will be set in stone until a few days before release.